1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly to a liquid crystal display panel that has spacers at desirable locations.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) controls the light transmittance of liquid crystal cells using an electric field to thereby display a picture on a liquid crystal display panel. To this end, the LCD includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix form, and driving circuits for driving the liquid crystal panel. The liquid crystal display panel is provided with pixel electrodes and a reference electrode, i.e. common electrode, to supply the electric field to each one of the liquid crystal cells. Usually, while each one of the liquid crystal cells on a lower substrate have an individual pixel electrode, the common electrode is formed as an integrated electrode for all of the liquid crystal cells across the entire surface of an upper substrate. Each pixel electrode is connected with a thin film transistor (TFT) that is used for a switching element. The pixel electrode together with the common electrode drives the liquid crystal cell in response to data signals supplied via the TFT.
FIG. 1 illustrates a simplified structure of a related art liquid crystal display panel. As shown in FIG. 1, a typical liquid crystal display panel includes coupled upper and lower array substrates 10 and 20, and liquid crystal material 8 between the upper and the lower array substrates 10 and 20. The liquid crystal material 8 rotates in response to an electric field supplied to thereby regulate the transmittance of incident light coming through the lower array substrate 20.
The upper array substrate 10 includes a color filter 4 and a common electrode 6 formed on the rear surface of the upper substrate 1. The color filter 4, where red (R), green (G), and blue (B) colored filter layers arranged in the form of stripe make it possible to display colors by selectively passing the light through these colored filters. A black matrix 2 is placed between the adjacent colored filters 4, and prevents the degradation of the contrast ratio by absorbing the light from the adjacent cells.
The lower array substrate 20 includes: a data line 18 and gate line 12 that are crossed and are insulated by a gate insulating layer formed on the entire surface of the lower substrate 21; a TFT 16 placed adjacent the crossing of the data and gate lines 18 and 12; and a pixel electrode 14 contacting the TFT 16. In response to gate signals from the gate line 12, the TFT 16 selectively supplies the pixel electrode 14 with data signals from the data line 18. The TFT 16 is composed of: a gate electrode connected to the gate line 12; a source electrode connected to the data line 18; and a drain electrode connected to the pixel electrode 14.
The pixel electrode 14 is made from transparent conductive material having high light transmittance, and is placed within the cell region defined by the data line 18 and gate line 12. Data signals supplied to the pixel electrode 14 via the drain electrode generate electric potential difference between the pixel and common electrodes 14 and 6. Under the influence of this electric potential difference, the liquid crystals residing between the upper and lower substrates 1 and 21 rotate due to the dielectric anisotropy thereof. Hence, the light supplied from a light source under the lower substrate 21 passes through the liquid crystals toward the upper substrate 1.
The cell gap between these upper and lower array substrates 10 and 20 is maintained by spacers, which are made through a manufacturing process illustrated in FIGS. 2a to 2d. As shown in FIG. 2a, mixed material of solvent, binder, monomer, and photo-initiator is printed onto a substrate 11. The mixed material is dried so as to evaporate the solvent such that a spacer material 26a is formed. The substrate 11 is either a lower substrate having TFTs and pixel electrodes installed thereon or an upper substrate having color filters installed thereon.
A photoresist 32 is coated on the substrate 11 having the spacer material 26a formed thereon. Then, a photomask MS is aligned, as shown in FIG. 2b. The photomask MS includes a mask substrate 34. A shielding layer 36 is formed on the mask substrate 34 so as to overlap with a shielding part S1. The transparent mask substrate 34 of the photomask MS is exposed at the exposure part S2. By carrying out the exposure process to selectively irradiate ultraviolet rays onto the photoresist 32 using the photomask MS and the development process to develop the exposed photoresist, a photoresist pattern 38 is formed, as shown in FIG. 2c. The spacer material 26a is patterned through an etching process using the photoresist pattern 38 as a mask, and consequently, a pattern spacer 26 having designated height is formed, as shown in FIG. 2d. 
The pattern spacer 26 of the related art LCD occupies only about 2% of the area of the substrate 11. More than 95% of the spacer material 26a that was been printed on the entire surface of the substrate 11 to form the pattern spacer 26 is removed during the subsequent processes of exposure, development, and etching. Thus, a lot of spacer material is wasted, which increases the costs of material and fabrication. Further, the additional mask process for forming the pattern spacer 26 including sub-processes, such as printing, exposure, development, and etching, leads to the problem of making the fabricating process even more complex.
In order to solve these problems, a fabricating method for the spacer using an ink-jet device has been suggested as shown in FIGS. 3a to 3c. First, as shown in FIG. 3a, an ink-jet device 40 is aligned so as to overlap with the location where the spacer is to be formed on the substrate 11. Here, the substrate 11 is either a lower substrate 21 having TFTs 16 and pixel electrodes 14 installed thereon or an upper substrate 1 having color filters 4 installed thereon. Then, the spacer material 26a is jetted onto the substrate 11 from the ink-jet device 40. In other words, when an external voltage is supplied to a piezoelectric element of the ink-jet head, physical pressure is generated. This physical pressure causes the conduit 44 connecting the tank 42 containing the spacer material 26a with the nozzle 46 to contract and relax repeatedly, and thereby the spacer material 26a is jetted to the substrate 11 through the nozzle 46, as shown in FIG. 3B.
The spacer 26 formed by the spacer material jetted through the nozzle 46 of ink-jet device thereafter undergoes an exposure to the ultraviolet ray radiated from a light source 48 or a firing process as shown in FIG. 3c, and then cures to have a width W and height H.
During the formation of the spacer using the related art ink-jet device, the spacer material 26a of low viscosity experiences the gravity while being jetted to the substrate 11. Due to the effect of gravity, upon arriving at the substrate 11 the spacer material 26a spreads out too widely and results in an undesirably small ratio of height H to width W. This leads to the problem of the spacer 26 being formed to overlap with the black matrix 2 so as to encroach into areas that are not overlapped with the black matrix 2, such as the display area, and appears as a stain on the display area.